70 Ophiuci with 70mm aperture

[Nik271]

I don't know how I've missed this one. It's a gem, two very unequal yellow-orange stars  6'' apart. 

I recently bought a 70mm F6 Svbony refractor which I mainly use for solar observation and I keep ready on a tripod in case there is a break in the clouds. It's a perfectly good performer in the night as well, on days when the forecast is iffy and I haven't put up a 'proper' scope. It has very little CA and gives sharp views on the Moon up to about x100.

Last evening was supposed to be cloudy but at 9:40pm the sky was clear! I focused on the setting Moon and started looking at the usual suspects which I can find in twilight.  Izar and the double double are near the limit of this small scope with a 4mm Nirvana (x105) , but the seeing was good and I could resolve them with careful observation.

 

Once it got a bit darker I began to spot brighter stars in the south sky:  Rasalgethi, Rasalhague, Calabrai, and I remembered a double star I read about recently: 70 Ophiuci. It's a close neighbour of ours, a pair of K-type stars just 16 light years away. I started from Calabrai with a 20mm EP giving a 3 degree field of view, no need of a finderscope. 70 Ophiuci is 5 degrees east from Calabrai among a bunch of other 4-th magnitude stars. At magnification x21 it looked like a single orange star. When I put in the 8mm BST for x53 it resolved into a pair of very unequal orange stars, the dimmer 6-th magnitude one being east from the primary. For this nearby system you can apparently observe orbital motion in a few years, the orbital period is 88 years. William Herschel who discovered it took note of the movement and argued correctly that it is the two stars orbiting each other, thus verifying Newton's law beyond our solar system. There were many conjectural companions and even planets claimed for this system over the years (Herschel himself suspected another companion) but nothing definite has been found so far.

Currently the pair are as far apart as they get, at 6.7''. They will start to close in and by 2076 they will be a serious challenge at 2'' apart. Not likely I will be there to worry about it 😉

 

 

Edited July 22, 2023 by Nik271
typo corrected

[The60mmKid]

3 hours ago, Nik271 said:

Currently the pair are as far apart as they get, at 6.7''. They will start to close in and by 2076 they will be a serious challenge at 2'' apart.

Something to look forward to 😎

[NGC 1502]

While you’re in that area of sky you are close to Barnard’s star, the star with the highest known Proper Motion. It’s a mag +9.5 red dwarf in the same low power field as 66 Ophiuchi.

On a moonless and transparent night I’ve bagged it with my 70mm Pronto from my light polluted back yard.

Well worth tracking down😊

Ed.

[Nik271]

On 25/07/2023 at 14:23, NGC 1502 said:

While you’re in that area of sky you are close to Barnard’s star, the star with the highest known Proper Motion.

Thanks for the suggestion, Ed! I saw Barnard's star several years ago with a Skymax 127, but forgot it's nearby.  I'll give it a try next clear night with the 70mm refractor. It's fun to revisit same targets with different telescopes, for a different perspective.

[Lorenzo]

Very beautiful 70 Ophiuco.
I first observed it in 1997 and a few months ago I remembered to check it out. And her secondary really moved. With the Aberrator program I created two images to make a gif with the movement of the couple. I observed them through the eyepiece. No photo.

Lorenzo